Expansion bolts typically include a body having a threaded portion for receiving a bolt and an expansible portion which expands when engaged by the threaded end of the bolt. Alternatively, an expansion bolt can include a plug or other element which is driven by the bolt to spread apart the expansible portion of the body. To use an expansion bolt to attach a component part to a base member, the expansible portion of the device is inserted in a hole that is formed in the base member. The bolt is installed to secure the body of the device to the base.
In general, expansion bolts primarily rely upon radial pressure and friction that is exerted on and by the wall of the preformed hole to keep the device and attached component parts secured to the base. Although often satisfactory, securement by radial pressure and friction can be undesirable when using the bolt in a relatively soft or impressible material such as wood. Specifically, expansion bolts often cause a wood base to split along the wood grain, especially if two or more expansion bolts are installed in relatively close proximity.
Various attempts have been made to provide an expansible fastening device that minimizes or eliminates cracking and splitting of the base member in which the device is installed. Although some progress has been reported, a need exists for a fastening device that can be firmly secured in wood or other such material in a manner that does not create crack-causing internal stress, yet achieves high strength fastening (i.e., substantial load bearing capabilities). To provide economical and widespread application, such a fastening device must be relatively inexpensive and easily used in a wide variety of fastening situations.